Controlled sensitivity, along with maximized energy content of energetic materials (EMs) remains an important aspect of materials engineering to guarantee explosives safety and function. The morphology of crystalline energetic materials, including crystal size, shape, microstructure, and purity of polymorphic phase, play a significant role in determining energetic materials performance, including their shock sensitivity. See M. Ghosh et al., Cryst. Growth Des. 14, 5053 (2014). Hexanitrohexaazaisowurtzitane (CL-20) is an EM compound containing six high energy nitro groups per molecule arranged into a strained cage structure that is capable of releasing vast amounts of stored energy through triggered rapid decomposition. See J. A. Bumpus, Adv. Phys. Chem., 175146 (2012). Since its first synthesis in 1989, CL-20 has been the most powerful non-nuclear EM available, ideal for applications in military grade propellants and explosives. See A. T. Nielsen et al., J. Org. Chem. 55, 1459 propellants and explosives. See A. T. Nielsen et al., J. Org. Chem. 55, 1459 (1990); and U. R. Nair et al., Combust. Explos. and Shock Waves 41, 121 (2005). Compared to the energetic properties of other commonly used EMs, CL-20 possesses more favorable properties including much larger heat of formation, better oxygen balance, and higher density. See M. B. Talawar et al., Combust. Explos. and Shock Waves 43, 62 (2007); and K. Liu et al., J. Mol. Struct. 1110, 91 (2016). For example, CL-20 shows a 14% higher explosive performance than cyclotetramethylene-tetranitramine (HMX) while maintaining nearly equivalent sensitivity. See R. L. Simpson et al., Propellants, Explos., and Pyrotech. 22, 249 (1997).
However, CL-20 powder prepared by existing methods consists of irregular crystalline particles. See J. Xu et al., J. Cryst. Growth 354, 13 (2012); Y. Bayat et al., J. Mol. Liquids 193, 83 (2014); Z. Yang et al., RSC Adv. 4, 65121 (2014); and J. H. Urbelis and J. A. Swift, Cryst. Growth Des. 14, 1642 (2014). Such irregularity in particle size and shape makes reproducibility and prediction of EM performance difficult. Additionally, detonation “hot spots” caused by sharp edges dramatically compromises EM stability. See M. Ghosh et al., Cryst. Growth Des. 14, 5053 (2014). Therefore, a need remains for CL-20 particles with small crystal size, spherical morphology and minimum crystalline defects.